This section provides background information related to the present disclosure which is not necessarily prior art.
The human or animal body has two lungs, each enclosed in a separate airtight area (pleural cavity) within the chest. If an object, for example bullet, shrapnel, knife, blast debris and/or stick penetrates the chest wall an open chest wound results, and allows air to enter one or both of the chest cavity area and the pleural cavity when the person next attempts to inhale. The lung will begin to collapse as a result of the loss of a pressure differential between the chest cavity area or pleural cavity and the air in the trachea, which is at outside pressure.
Any degree of collapse of either lung interferes with the casualty's ability to breath and reduces the amount of oxygen available for use by the body.
It is therefore important, in cases of actual or suspected penetrating thoracic trauma, to apply a dressing that prevents the ingress of air, through the wound in the chest wall, into the chest cavity area or pleural space.
However, if the lung has also been punctured, then air may also enter the pleural space via that route and if not allowed to escape may result in an increase in pressure again resulting in a serious impairment (life threatening) to breathing. The latter case is known as a tension pneumothorax.
Fluids, for example blood, resulting from the trauma may also leak into the pleural space and need to be able to escape.
Consequently any dressing applied to an actual or suspected penetrating chest wound needs to allow the egress of air and fluid from the pleural space but also prevent the ingress of air and fluid.
A number of dressing constructions have been proposed to address this issue.
In U.S. Pat. No. 5,195,977 (assigned to Lohman GmbH & Co), the disclosure of which is incorporated herein by reference, a wound dressing (plaster) is described which has a gas check valve which responds to slight pressure variations. The gas check valve is inserted in an aperture in the plaster. The skin facing side of the plaster is coated with a pressure sensitive adhesive. The gas check valve may be of a diaphragm, ball, plug or spring type. No exemplification of the slight pressure variation required to activate the valve is given. The pressure sensitive adhesive used is described as a rubber adhesive or an acrylic adhesive.
U.S. Pat. No. 5,160,322 (assigned to Brunswick Biomedical Technologies Inc.), the disclosure of which is incorporated herein by reference, describes a one-way valve which permits the outward flow of air and liquid from the chest cavity but closes against the same flow of atmospheric air into the chest cavity. A dome protruding from the outward facing surface of the dressing protects the valve element.
U.S. Pat. No. 7,615,674 (Asherman), the disclosure of which is incorporated herein by reference, describes a dressing comprising a one way valve which is rigid to prevent obstruction of the valve arising from turning of the patient's clothing.
U.S. Pat. No. 7,429,687 (assigned to The Seaberg Company Inc.), the disclosure of which is incorporated herein by reference, describes an adhesively attachable bandage comprising a valve assembly with a rigid cover. The adhesive is preferably an aggressive hydrogel or hydrocolloid possessing good wet tack and so are able to adhere to damp skin. However, no description is provided for specific examples of suitable materials.
U.S. Pat. No. 5,478,333 (Asherman), the disclosure of which is incorporated herein by reference, describes a dressing comprising a flexible body with adhesive on one side for attaching the body to the skin of the patient. The centre of the body is formed into a flexible tubular duct which projects away from the patient. A flexible one way valve is mounted to the exterior of the duct to allow the passage of air fluid out of the wound but preventing air being drawn back into the wound through the duct.
U.S. Pat. Application 2008/0234726 A1, the disclosure of which is incorporated herein by reference, describes a chest seal dressing with a low profile one way valve also comprising a biocompatible adhesive. Suitable adhesives for adhering the flange body to the patient's skin include hydro gel, acrylic, silicone gel, silicone PSA or hydrocolloid. No specific examples are disclosed. The passage of fluid is not described.
Due to the complexity of the valve arrangements disclosed in the prior art the cost of these dressings is high. In addition, the valve constructions in all of the above prior art systems have a substantially greater thickness than the skin-adhesive portions of the dressing in the major face to major face direction of the dressing, and have hard or rigid portions which can press into the wound if the patient's weight or some external force presses on the dressing. Some of the valves (e.g., the valve of U.S. Pat. No. 5,478,333 to Asherman) can become closed permanently simply by the patient lying awkwardly.
WO-A-2005/039465, the disclosure of which is incorporated herein by reference, describes an attempt to solve at least some of the above problems. The dressing described has a bandage section which overlies the wound and is sealed to the skin around a perimeter to enclose a space above the wound, and a single flutter valve mouth which provides one-way fluid flow communication between the space above the wound and the exterior environment. The valve lies substantially in the same plane as the bandage section. Nevertheless, the valve of this prior art is still bulky in that at least four sheets of material (FIG. 6) are required for its construction, and a rigid outer casing is specified as most preferred (page 4, lines 19 to 23; page 11, lines 9 to 16). Embodiments in which an additional fluid inlet valve is provided for flushing-out the flutter valve are described, which is no longer planar with the remainder of the device (FIGS. 8 to 10).
There is general concern that chest seals used for treatment of open chest wounds can fail due to coagulation or malfunction of the external vent and poor skin adherence. Chest seal failure may lead to respiratory compromise or the development of a tension pneumothorax. (Arnaud F. et al., Evaluation of chest seal performance in a swine model: comparison of Asherman vs. Bolin seal. Injury, 2008 September; 39(9):1082-8.). The disclosure of this publication is incorporated herein by reference.
Dressings adapted to permit essentially one way fluid flow away from a wound may also find use in special circumstances, such as where a managed flow of blood from a wound, or a managed restriction or prevention of contact between external sea water and the wound is required.
The present invention as described below provides an alternative, and improved dressing, over those disclosed in the prior art. The present invention may overcome or mitigate at least one or more problems associated with the dressings of the prior art.